As alternatives to the standard estrogen pharmaceuticals used for hormone replacement therapy, many older women are using botanical estrogens to treat menopausal symptoms, believing that these dietary supplements are inherently safe because they are natural. Also, because of improved therapies, many breast cancer survivors are living for many years after their breast cancer arises, and a significant number of these women are using these botanicals in the hope that they will help in managing their disease. The overall goal ofthis project is to evaluate the activity of botanical estrogens on important estrogen target tissues and on breast cancer metastasis. In Aim 1, we will investigate the effects of botanical estrogens (from soy, wild yam, licorice root, and dong quai) on three important target tissues, bone, uterus, and mammary gland, in mice and rats, comparing their effects with that of known estrogens, estrogen receptor subtype-selective ligands, and selective estrogen receptor modulators. In Aim 2, we will evaluate the effects of botanical estrogens on the growth and progression of breast cancer in bone and subsequent metastasis to lung and other visceral sites, in a pre-clinical animal model using in vivo bioluminescence imaging, pathological and histological examination, and analysis of gene expression profiles that correlate with metastatic activity. These findings could be relevant to human health, because metastases to bone and lung are major routes of breast cancer expansion in women and contribute greatly to morbidity and mortality. Botanicals, extracts, fractions and pure isolates will be obtained from Core A, with doses determined by Core B. The work in this project will benefit from the results of the mechanistic studies on the botanical estrogens in Project 1 and will interface with the studies on bone health in older animals obtained from Project 3. Collectively, results from these studies will enable determination ofthe effects of botanical estrogens on estrogen target tissues in pre-clinical rodent models and on cancer progression and metastasis in a mouse model. These findings will be important in understanding the actions and safety of botanical estrogens used by women.